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Scott W. Yeates, Loretta B. Szczotka-Flynn, Ashraf M. Mahmoud, Cynthia J. Roberts; Corneal Topographic Changes During Continuous Silicone Hydrogel Contact Lens Wear. Invest. Ophthalmol. Vis. Sci. 2011;52(14):6473.
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To assess whether continuous wear (CW) with silicone hydrogel (SH) lotrafilcon A contact lenses induces changes in Orbscan II-derived corneal topographic indices.
Subjects were fitted with lotrafilcon A lenses for monthly CW and observed for 1 year. Orbscan II measurements of right eyes were taken at baseline, and after 1 week (n=151), 1 month (n=151), and 1 year (n=85) of wear. Slit images were reprocessed using a beta version (v 3.12) edge tracker software and the following indices were evaluated: anterior steep and flat simulated keratometry (simK), posterior corneal best fit sphere, posterior corneal elevation, and pachymetry at the thinnest 0.5mm corneal spot. Paired T-tests were utilized stratified by type of contact lens worn at study entry.
No changes were noted in posterior corneal indices or pachymetry over time. For the entire cohort, significant changes were noted for anterior steep and flat simK values after 1 week of CW. Average steep simK flattened by 0.20 D (p=0.0016, range -4.14 to +2.79 D), 0.27 D (p<0.0001, range -4.11 to +2.82 D), and 0.29 D (p=0.003, range -5.12 to +1.78 D), after 1 week, 1 month and 1 year, respectively. Stratified by pre-study contact lens use, neophytes (n=47) showed no simK changes over time; SH lens wearers (n=24) showed the greatest amount of corneal flattening of 0.44 D, 0.38 D, and 0.59 D after 1week, 1 month and 1 year, respectively (p<0.007); and low Dk lens users (n=71) had significant flattening at all time points of 0.21 D, 0.35 D and 0.30 D after 1 week, 1 month, and 1 year respectively, (p<0.039) and the greatest variability of all groups (range -5.12 D to +2.87 D).
CW of lotrafilcon A lenses did not alter the thinnest pachymetry, posterior corneal elevation or posterior best fit sphere in this sample. Subjects switching from low Dk lenses had the greatest variation in simK values, but subjects switching from other SH lens types had the greatest amount of average corneal flattening. These findings are valuable for clinicians when monitoring patients for refractive shifts during SH contact lens CW.
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